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Action potential propagation

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Physiology 3120
Tom Stavraky

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Human Physiology Friday, October 2, 2009 Propagation of Action Potentials • Generally, begins at axon hillock, and flow orthodromically down the axon to the nerve terminus  Current flows from positive to negative  During AP, current carried by positive ions • Non-myelinated neurons  Diagram on EC-65 shows cathodal electrode (i.e. attracts positive charges)  Regions adjacent to original AP become depolarized as the positivity inside the cell spreads in both directions  Causes the action potential to occur in adjacent regions  In vivo, action potential only travels in one direction because of refractory periods  Action potentials stays all-or-none all along the axon • Myelinated neurons  Insulated by myelin which is produced by. . .  Schwann cells (peripheral)  Oligodendrocytes (CNS)  Myelin increases resistance across membrane by about 5,000 times, so ions won’t move across membrane where there is myelin  Voltage-gated channels located at nodes of Ranvier only  Use saltatory conduction
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